However, if you scrub through the time line, you'll notice that the particles fall away from the plane which, to state it mildly, is less than ideal. To fix this, simply check the box called Lock On Emitter and the particles will stay in position (Fig.13).

Fig. 13

This is all good of course, but at this point the particles are placed completely randomly and in a city with streets, this isn't very realistic. To fix this, you first need to create a black and white material for the CityEmitter. Light areas will receive the highest density of particles while completely dark areas will receive none. In the example, I've combined the procedural textures Tiles and Gradient Ramp to create a texture, but you could also paint one in Photoshop or similar to get a more organic distribution map (Fig.14).

Fig. 14

Back in Particle View and still under Position Object, scroll down to Location and check the box called Density By Material. The particles are now concentrated in the lighter areas (Fig.15).

Fig. 15

To make sure the buildings don't stand on top of each other also check Separation and play with the Distance until the particles have some space between them (Fig.16).

Fig. 16

Fig. 17

Step 2.3: Speed

Buildings really shouldn't move around that much, so the speed controller is useless here. Right click it and choose Delete (Fig.17).

Fig. 17

Step 2.4: Shape

Now we're going to replace the rather boring-looking ticks with the actual building. Clicking on the Shape controller doesn't give us a whole lot of options so we clearly need another one: Shape Instance. Replace Shape with Shape Instance the same way you replaced Position Icon above (Fig.18).

Fig. 18

Then, with Shape Instance selected, press the button called None under Particle Geometry Object and choose a building by pressing H on the keyboard. I'll pick my SkyScraper object (Fig.19).